ASSESSMENT OF RESIDUAL LIFE OF GIRDERS OF BRIDGE No

Life = 120 / k1 m = 594 years
Remaining Life = 594 – 66 = 528 years
Calculated Residual Life of girders in different conditions are shown below:
S Traffic Type Residual Life in years for Traffic Density
.No.
42 – 27 GMT 27 – 18 GMT 18 – 12 GMT
1 Heavy Traffic 22 76 139
2 Medium Traffic 82 145 238
3 Light Traffic 225 412 528
5.2 Assessment of residual life with damage calculation: . It may be used as a
more precise alternative to the simplified procedure as described in para.5.1
above. This method involves a calculation based on Miner’s summation rule.
S.N. curve developed for limited number of fatigue testing of specimen taken out
from the existing girders and stress cycles are computed from the data as shown
in para 4.2.4 of this report. The calculation of residual life of the girders based on
the loading spectrum of the Ganga bridge for traffic density of 27 GMT, is shown
below:
Stress range in
N/mm 2
Mean Stress
Range in
N/mm 2
13
No. of cycles
per day
No. of cycles as
per SN curve X
10 6
96.250-86.625 91.4375 32 3.19
67.375-57.750 62.5625 62 18.16
38.500-28.875 33.6875 38 315.06
Damage per Year (D) =∑ (ni/Ni)
=[(32/3.19)+(62/18.16)+(38/315.06)]x10 -6
=0.005
Residual Life = 0 .3/D
= 60 years
6.0 Observations:
It is observed from the method of assessment of residual fatigue life, without
damage calculation that residual life of the girders is more conservative as the
minimum residual life calculated is 22 years for heavy traffic (42-27GMT) and the
maximum residual life is 528 years for light traffic (18-12GMT). However, based
on load spectrum as per Indian Rly’s traffic pattern the residual life as per
damage calculation method is 60 years for traffic density of 27 GMT. It seems to
be more realistic. The residual life, for lighter traffic conditions. By considering
the fact that the residual life varies inversely with the traffic density, the
relationship between residual life and traffic density can be drawn on log-log